Slicing a cake across layers is about prioritising value and mitigating the risk of building the wrong thing. Most product and feature requirements are hypothesis for creating value, unless that hypothesis has already been validated.

> It's very convenient for the stakeholders to see progress mapped out like that It's important for the business to validate product value. This is not just progress anxiety.

Crafting software to perfection is ultimately a waste if it doesn't provide value to the business or customer. If we are sure we're building the right thing, we can risk more, and spend more of our time building the thing better. Build scrappy first, build confidence in value, and then craft to perfection.

The slices of cake aren't built in isolation. Every time a slice is being worked on, it is integrated back. The cake analogy falls apart here, because cakes (and houses) aren't nearly as malleable as software. We have opportunities to refactor it every step along the way, and change its shape. Yes, sometimes we refactor independent of business value, and I think that's essential too. I don't think the idea that's presented is to have absolutely every slice be vertical, and business / customer facing.